THIS FILE CAN HELP YOU LEARN A BIT OF WHATS THE EARTH LIKE THAT

1. HISTORY OF LIFE ON EARTH
December 5 & 7,2017

2. TODAY’S LESSON
1. How old is the Earth?
2. Geologic Time School
3. Fossils

3. PART 1: HOW OLD IS THE EARTH
1. What is the age of the Earth? The Earth is 4.6 billion years
old. Life on Earth arose around 3.5 billion years ago.
2. What was the Earth like million of years ago? (1) covered
with thick blanket of ice, (2) lots of volcanoes and high
mountains, (3) large organisms roamed the land, (4) the
atmosphere did not have high oxygen content, (4)
asteroids/ meteors frequently hit the surface, (5) the lands
moved a lot or the continents were a little closer to each
other, (6) volcanic eruptions, (7) a little bit warmer, (8)
plants were bigger, (9) humans were not yet around. Over
Earth’s vast history, both gradual and catastrophic
processes have produced enormous changes.

4. PART 1: HOW OLD IS THE EARTH
3. When did man first appear on Earth? Humans did not co-
exist with dinosaurs as what movies usually depict. Man
could have appeared about 100-150 thousand by
artefactual evidences in various sites. The human timeline
is rather flexible and debatable. Every time we know a
specific date, a new discovery date is announced and
everything gets re-dated to fit the best estimates.

5. UNLOCKING OF TERMS
1. EON- largest division of the geologic time scale;
spans hundreds to thousands of million of years
ago (mya)
2. ERA- division in an Era that span time periods of
tens to hundreds of millions of years
3. PERIOD- a division of geologic history that spans
no more than one hundred million years
4. EPOCH- the smallest division of the geologic time
scale characterized by distinctive organisms

6. PART 2: GEOLOGIC TIME SCALE
The Geologic time is divided into four large segments
called Eons: Hadean, Archean, Proterozoic and
Phanerozoic. The Phanerozoic is divided into Eras:
Paleozoic, Mesozoic, and Cenozoic. Extinction events
and appearance of new life forms characterized the
divisions among Eras. Smaller divisions, called Periods,
characterized by a single type of rock system, make
up each Era. Some Periods are further divided into
smaller time frame called Epochs.

8. PART 2: GEOLOGIC TIME SCALE
The Geological Time Scale (GTS)
A. Four eras - Precambrian; Paleozoic; Mesozoic; Cenozoic
B. Periods under the Paleozoic era - Cambrian, Ordovician,
Silurian, Devonian, Carboniferous, Permian
C. Periods under the Mesozoic era - Triassic, Jurassic,
Cretaceous
D. Periods under the Cenozoic era - Tertiary and Quaternary
*Age in millions of years of each time period

9. PART 3: FOSSILS
FOSSILS are evidences of organisms that lived in the past. They
can be actual remains like bones, teeth, shells, leaves, seeds,
spores or traces of past activities such as animal burrows, nests
and dinosaur footprints or even the ripples created on a
prehistoric shore.
* In exceptional preservation, fine details such as original color
and individual muscle fibers are retained, features often visible
in electron microscopes. This is referred to as the “Medusa
effect.”

10. PART 3: FOSSILS
TYPES OF FOSSILS DESCRIPTION EXAMPLES
Molds Impression made in a substrate =
negative image of an organism
Shells
Casts When a mold is filled in Bones and Teeth
Petrified Organic material is converted into
stone
Petrified trees;
Coal balls (fossilized plants
and their tissues, in round
ball shape)
Original Remains Preserved wholly (frozen in ice,
trapped in tar pits, dried/ desiccated
inside caves in arid regions or
encased in amber/ fossilized resin)
Woolly mammoth;
Amber from the Baltic Sea
region
Carbon Film Carbon impression in sedimentary
rocks
Leaf impression on the rock
Trace / Ichnofossils Record the movements and
behaviors of the organism
Trackways, toothmarks,
gizzard rocks, coprolites
(fossilized dungs), burrows
and nests

11. PART 3: FOSSILS
THE SIX WAYS OF FOSSILIZATION
1. Unaltered preservation - Small organism or part trapped in
amber, hardened plant sap
2. Permineralization/ Petrification - The organic contents of bone
and wood are replaced with silica, calcite or pyrite, forming a
rock-like fossil
3. Replacement - hard parts are dissolved and replaced by other
minerals, like calcite, silica, pyrite, or iron
4. Carbonization or Coalification - The other elements are removed
and only the carbon remained
5. Recrystalization - Hard parts are converted to more stable
minerals or small crystals turn into larger crystals
6. Authigenic preservation - Molds and casts are formed after most
of the organism have been destroyed or dissolved

12. PART 3: FOSSILS
DATING FOSSILS
Knowing the age of a fossil can help a scientist establish its position in the geologic
time scale and find its relationship with the other fossils. There are two ways to
measure the age of a fossil: relative dating and absolute dating.
1. RELATIVE DATING
I. Based upon the study of layer of rocks
II. Does not tell the exact age: only compare fossils as older or younger, depends
on their
III. position in rock layer
IV. Fossils in the uppermost rock layer/ strata are younger while those in the
lowermost
V. deposition are oldest
How Relative Age is Determined
I. Law of Superposition: if a layer of rock is undisturbed, the fossils found on
upper layers are younger than those found in lower layers of rocks
II. However, because the Earth is active, rocks move and may disturb the layer
making this process not highly accurate

13. PART 3: FOSSILS
RULES OF RELATIVE DATING
A. LAW OF SUPERPOSITION: Sedimentary
layers are deposited in a specific time-
youngest rocks on top, oldest rocks at
the bottom
B. LAW OF ORIGINAL HORIZONTALITY:
Deposition of rocks happen horizontally-
tilting, folding or breaking happened
recently
C. LAW OF CROSS-CUTTING
RELATIONSHIPS: If an igneous intrusion
or a fault cuts through existing rocks, the
intrusion/fault is YOUNGER than the rock
it cuts through

14. PART 3: FOSSILS
2. ABSOLUTE DATING
I. Determines the actual age of the fossil
II. Through radiometric dating, using radioactive isotopes carbon-14
and potassium-40
III. Considers the half-life or the time it takes for half of the atoms of
the radioactive element to decay
IV. The decay products of radioactive isotopes are stable atoms.
*CARBON-14 DATING; A living organism has carbon-14. For the amount of
Carbon in the organism’s body to become half, it will take about 5,700 years;
which is the half-life of carbon-14.
*INDEX FOSSILS (guide fossils/ indicator fossils/ zone fossils): fossils from
short-lived organisms that lived in many places; used to define and identify
geologic periods